Alias sampling for IF-to-baseband conversion in a GPS receiver

• US 7,099,406 B2
• Filed: 08/30/2002
• Issued: 08/29/2006
• Est. Priority Date: 08/30/2002
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: RF Micro Devices Incorporated (Qorvo, Inc.)
• Inventors: Keegan, Richard, Najarian, Richard
• Primary Examiner(s): Ha, Dac
• Assistant Examiner(s): Joseph, Jaison
• Application Number:
  US10/232,650
• Publication Number:
  US 20040042563A1
• Time in Patent Office: 1,460 Days
• Field of Search: 375/316, 375/148, 375/150, 375/134, 375/149, 342/90, 455/12.1, 455/427, 455/131, 455/313, 455/323, 455/333
• US Class Current: 375/316
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/32 Multimode operation in a single same satellite system, e.g. GPS L1/L2
• CPC Class Codes: G01S 19/36 relating to the receiver frond end
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain

Abstract

The present invention provides a GPS receiver comprising sampling circuitry adapted to perform IF-to-baseband conversion. In general, the GPS receiver includes downconversion circuitry that uses a first synthesizer output signal to reduce an amplified GPS input signal to an intermediate frequency signal, and sampling circuitry that receives the intermediate frequency signal and produces a baseband digital representation of the amplified GPS input signal. The sampling circuitry performs IF-to-baseband conversion by using a sampling rate equal to the frequency of a second synthesizer output signal, where the sampling rate is selected such that only an alias of the IF signal having the appropriate baseband frequency is digitized.

Claims

1. A GPS receiver comprising:

downconversion circuitry adapted to receive an amplified GPS input signal and a first synthesizer output signal at 272F and produce an IF signal from said amplified GPS input signal; and

sampling circuitry having a sampling rate equal to a frequency of a second synthesizer output signal at 8.5F and adapted to receive said IF signal and said second synthesizer output signal and produce a digitized signal using alias sampling, wherein said digitized signal contains GPS information carried in said amplified GPS input signal and F is 5.115 MHz.

2. The GPS receiver according to claim 1 wherein said amplified GPS input signal is a L1 GPS signal at 308F after amplification, said IF signal has a center frequency of 36F, and said digitized signal has a center frequency of 2F.

3. The GPS receiver according to claim 1 wherein said amplified GPS input signal is a L2 GPS signal at 240F after amplification, said IF signal has a center frequency of 32F, and said digitized signal has a center frequency of negative 2F.

4. The GPS receiver according to claim 1 wherein said amplified GPS input signal is a combination of a L1 GPS signal at 308F and a L2 GPS input signal at 240F, said IF signal has a 36F component and a 32F component, and said digitized signal has a center frequency of 2F or negative 2F depending on filtering of said IF signal prior to digitization.

5. The GPS receiver according to claim 1 wherein said digitized signal is a fourth alias of said IF signal.

6. The GPS receiver according to claim 1 wherein said sampling circuitry comprises an analog-to-digital converter adapted to produce said digitized signal.

7. The GPS receiver according to claim 6 wherein said sampling circuitry further comprises an anti-alias filter operatively associated between said downconversion circuitry and said analog-to-digital converter and adapted to remove unwanted frequencies from said IF signal thereby preventing aliases of said unwanted frequencies from appearing in said digitized signal.

8. The GPS receiver according to claim 1 wherein said downconversion circuitry and said sampling circuitry are integrated into a single semiconductor die.

9. The GPS receiver according to claim 8 wherein said semiconductor die is fabricated using a SiGe semiconductor process.

10. The GPS receiver according to claim 1 further comprising a frequency synthesizer operatively associated with said downconversion circuitry and said sampling-circuitry and adapted to provide said first and second synthesizer output signals wherein said frequency synthesizer is driven by a reference oscillator.

11. The GPS receiver according to claim 1 wherein said downconversion circuitry and said sampling circuitry are adapted to receive differential input signals to suppress received noise.

12. The GPS receiver according to claim 1 further comprising a low noise amplifier operatively associated before said downconversion circuitry and adapted to amplify a GPS input signal, which when filtered provides said amplified GPS input signal.

13. The GPS receiver according to claim 1 further comprising GPS signal processing logic operatively associated with said sampling circuitry and adapted to receive said digitized signal and extract said GPS information from said amplified GPS input signal.

14. The GPS receiver according to claim 1 further comprising filtering circuitry operatively associated between said downconversion circuitry and said sampling circuitry, wherein said filtering circuitry is adapted to remove unwanted frequency components from said IF signal.

15. The GPS receiver according to claim 14 wherein said filtering circuitry comprises a SAW filter.

16. The GPS receiver according to claim 14 further comprising first gain logic operatively associated between said downconversion circuitry and said filtering circuitry and second gain logic operatively associated between said filtering circuitry and said sampling circuitry, wherein said first gain logic is adapted to amplify said IF signal and provide said filtering circuitry with a signal having sufficient input power, and said second gain logic is adapted to provide said sampling circuitry with a filtered signal having sufficient input power.

17. A semiconductor die comprising:

downconversion circuitry adapted to receive an amplified GPS input signal and a first synthesizer output signal at 272F and produce an IF signal from said amplified GPS input signal; and

sampling circuitry having a sampling rate equal to a frequency of a second synthesizer output signal at 8.5F and adapted to receive said IF signal and said second synthesizer output signal and produce a digitized signal using alias sampling, wherein said digitized signal contains GPS information carried in said amplified GPS input signal and F is 5.115 MHz.

18. The GPS receiver according to claim 17 wherein said amplified GPS input signal is a L1 GPS signal at 308F after amplification, said IF signal has a center frequency of 36F, and said digitized signal has a center frequency of 2F.

19. The GPS receiver according to claim 17 wherein said amplified GPS input signal is a L2 GPS signal at 240F after amplification, said IF signal has a center frequency of 32F, and said digitized signal has a center frequency of negative 2F.

20. The GPS receiver according to claim 17 where in said amplified GPS input signal is a combination of a L1 GPS signal at 308F and a L2 GPS input signal at 240F, said IF signal has a 36F component and a 32F component, and said digitized signal has a center frequency of 2F or negative 2F depending on filtering of said IF signal prior to digitization.

21. The semiconductor die according to claim 17 wherein said digitized signal is a fourth alias of said IF signal.

22. The semiconductor die according to claim 17 wherein said sampling circuitry comprises an analog-to-digital converter adapted to produce said digitized signal.

23. The semiconductor die according to claim 22 wherein said sampling circuitry further comprises an anti-alias filter operatively associated between said downconversion circuitry and said analog-to-digital converter and adapted to remove unwanted frequencies from said IF signal, thereby preventing aliases of said unwanted frequencies from appearing in said digitized signal.

24. The semiconductor die according to claim 17 wherein said semiconductor die is fabricated using a SiGe semiconductor process.

25. The semiconductor die according to claim 17 further comprising a frequency synthesizer operatively associated with said downconversion circuitry and said sampling circuitry and adapted to provide said first and second synthesizer output signals wherein said frequency synthesizer is driven by a reference oscillator.

26. The semiconductor die according to claim 17 wherein said downconversion circuitry and said sampling circuitry are adapted to receive differential input signals to suppress received noise.

27. The semiconductor die according to claim 17 further comprising a low noise amplifier operatively associated before said downconversion circuitry and adapted to amplify a GPS input signal, which when filtered provides said amplified GPS input signal.

28. The semiconductor die according to claim 17 wherein said sampling circuitry is operatively associated with GPS signal processing logic adapted to receive said digitized signal and extract said GPS information from said amplified GPS input signal.

29. The semiconductor die according to claim 17 further comprising connections for external filtering circuitry operatively associated between said downconversion circuitry and said sampling circuitry, wherein said external filtering circuitry is adapted to remove unwanted frequency components from said IF signal.

30. The semiconductor die according to claim 29 wherein said filtering circuitry comprises a SAW filter.

31. The semiconductor die according to claim 29 further comprising first gain logic operatively associated between said downconversion circuitry and said connections and second gain logic operatively associated between said connections and said sampling circuitry, wherein said first gain logic is adapted to amplify said IF signal and provide said external filtering circuitry with a signal having sufficient input power, and said second gain logic is adapted to provide said sampling circuitry with a filtered signal having sufficient input power.